Apparatus for applying a dispersion coating to a surface, such as a tape



Feb. 19, 1963 R. 5. 000K 3,077,359

APPARATUS FOR APPLYING A DISPERSION COATING TO A SURFACE, SUCH AS A TAPEFiled Nov. 4, 1958 2 Sheets-Sheet l VACUUM INVENTOR R. 5. COOK BYATTORNEY Feb. 19, 1963 'R. s. COOK 3 07 APPARATUS FOR APPLYING ADISPERSION COATING TO A SURFACE, SUCH AS A TAPE Filed Nov. 4, 1958 2Sheets-Sheet 2 CARRIER AIR STREAM PAIN T-A/R STREAM DEFLEC 7' IONAIR-STREAM A/R STREAM lNVENTOR R. S. COOK Afro/Mg United States Patent 3077,859 APPARATUS FOR APPLYING A DISPERSION COATING TO A SURFACE, SUCHAS A TAPE Robert 5. Cook, Morristown, vN.J., assignor to BellTele phoneLaboratories, Incorporated, New York, N.Y,.,

a corporation of New York Filed Nov. 4, 1958, Ser. No. 771,922 3 Claims.(Cl. 118326) This invention relates to a method of, and apparatus for,forming dispersion coatings and, more particularly, to a self-enclosedspray system for forming dispersion coatings of uniform thickness anddensity.

The formation of dispersion coatings on various ob- 'jects is ofinterest in many different processes and types of equipment. Oneimportant field of interest is the fabrication of magnetic recordingdrums each having a multiplicity of'recording tracks which have theirexternal surfaces formed by magnetic dispersion coatings. It isdesirable that these recording tracks should be made in such a mannerthat they will have high recording sensitivity and will provide goodsignal reproduction with satisfactory signal-to -noise. ratio. Thesecharacteristics are determined by such factors as the thickness of therecording tracks and the degree of uniformity of the distribution anddensity of the metallic particles which form the magnetic coatings onthe, tracks since the inherent magnetic noise amplitude is somewhatproportional to these conditions in different unit areas of the tracks.

Accordingly, it is an object of this invention to provide an improvedmethod and meansfor forming dispersion coatings. I I

Another object of the invention is. to provide an improved self-enclosedspray system for forming dispersion coatings of uniform thickness anddensity.

It is also an object of this invention to provide. an improvedself-enclosed spray system having a controlled environment for formingan evenly dispersed coating on a selected portion of the surface of anobject without the necessity for masking other portions of this surface.

These and other objects of the invention are, accomplished by employingan air brush for directing a coneshaped spray of fine particles into oneend of a small chamber having its other end provided with an outputopening adapted to be placed adjacent to an object which is to becoated. The chamber is provided with air ducts or deflection tubes onopposite sides thereof near the output opening. Air supplied throughthese ducts serves to reshape the spray by spreading its center so as toprovide more even dispersion of the particles. The chamber is furtherequipped with a vacuum source for controlling the rate of entry of aircoming into the chamber from the deflection tubes. The vacuum sourcealso functions to draw out or remove any particles of the spray materialwhich do notstick to the object to becoated.

These and other features of the invention are more fully discussed inconnection with the following detailed description of the drawing inwhich:

FIG. 1 is a perspective view of one embodiment of an improvedself-enclosed spray system in accordance with this invention andillustrating the manner in which it is positioned against a recordingtrack;

FIG. 2 is a three-dimensional view partly in section of the spray systemand showing its internal construction; and

FIGS. 3A, 3B, and 3C, are schematic dia rams representing thedistribution and concentration of the coating material in the air streamat those points in the spray system that are indicated by the referencecharacters A, B, and C in FIG. 2.

In FIGS. 1 and 2, the spray system is shown to include a chamber 1formed by a rectangular housing 2.

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The chamber 1 is provided at one end with an input opening 3 constitutedby the projecting endof a hollow cylindrical tube 4 which extendslongitudinally through the chamber 1. Adjacent tothis input opening 3 isa conventional air brush 5 which is mounted in any convenient manner,such as upon a bracket 6 which may be an extension of the bottom of thehousing 2. The air brush 5 is equipped with an input 7 for supplyingpressurized air and another input 8 for supplying the material which isto form the dispersion coating.

The chamber 1 is provided at its opposite end with a relatively largeoutput opening 9 which, if desired, may be shaped in the mannerindicated in the drawing so as to fit snugly against the particularobject thatis to be coated. This object may, for example, be a magneticrecording tape 10 in which case the output opening 9 may be so shaped asto enclose a portion of the snrfaceof the tape 10. By thus enclosing thesurface to which the dis- .persion coating is to be applied, the escapeof fumes or off-spray particles is prevented. In addition, thisconstruction avoids the necessity for masking or covering any adjacentsurface area which is not to be coated.

As is indicated in the drawing, the tube 4 extends through the chamber 1almost to the output opening 9 .but terminates at short distancetherefrom. This end portion of the tubeA is intersected on oppositesides there- 'of by two air ducts 11 and 1-2 which function asdeflection tubes in a manner that is explained hereinafter. These airducts 11 and 12 project through opposite sidesjof th housing 2 in themanner illustrated in the drawing.

An opening 13 is cut in the bottom of the chamber 1 for admitting oneend of a pipe'or hose 14 which is connected to a conventional adjustablevacuum source. As was stated above, the vacuum thus supplied serves tocontrol the rate of entry of air coming into the chamber 1 through theair ducts 11 and 12. It is to be noted that the opening 13 is so locatedthat it is nearer to. the input end of the chamber 1 than it is to theoutput end of the chamber 1. By thus separating the vacuum opening 13from the output opening 9 of the chamber 1, undesirable turbulence ofthe air stream is avoided.

This spray system may be mounted in a stationary manner in which casethe object to be coated would be placed against the output opening 9.When this object is in the form of a magnetic recording tape, such asthe tape 10, it can be moved at a uniform rate of speed across theopening 9, such as in the direction of the arrows shown in FIG. 1, whileit is receiving the dispersion coating.

If it should be desirable for the object to remain stationary, then thespray system can be moved over it at a constant rate of speed by meansof a handle 15 which may be attached to the bottom of the housing 2,When the spray system is to be used in this manner. it should be placedclosely against the surface that is to be coated. This handle 15 may bein the shape of a pistol grip, as

is represented in FIG. 1, and may be fabricated of any suitablematerial, such as molded plastic material. As a matter of convenience,the handle 15 may be'formed in a hollow manner so that the vacuum hose14 can extend therethrough as is shown in FIG. 1.

It is to be understood that the spray system of this invention may beemployed for forming evenly dispersed coatings of fine particles ofvarious substances .on different kinds of objects. As was stated above,one important field of use is the production of magnetic coatings onmagnetic recording drums or tapes. When the invention is used for thispurpose. the input 8 of the air brush 5 is connected through aconventional'circulation system to a receptacle containing appropriatematerial for forming the magnetic dispersion coating. This material maybe a paint-like compound of very fine particles of magnetic material,such as a suitable magnetic oxide, thoroughly mixed with a binder, suchas lacquer, and a solvent or thinner for keeping the components in astable solution. As this magnetic paint enters the air brush 5, it isatomized by pressurized air supplied through the input 7 with the resultthat the air brush produces a narrow cone-shaped spray of extremelysmall droplets of paint.

At the time when this cone-shaped spray of paint droplets enters theinput opening 3 of the chamber 1, the vacuum source 13 draws in throughthe input opening 3 a carrier air stream, as is represented in FIG. 2,which blends with t e paint spray output from the air brush 5. Thevacuum source 13 causes the resulting paint-air stream to flow throughthe passage defined by the tube 4 toward the output opening 9 at such avelocity as to control the spreading of the cone-shaped spray so thatits full diameter is not reached until it is about to enter the areainfluenced by the deflection tubes 11 and 12. Before reaching thispoint, the paint-air stream will have at some earlier point, such as thepoint indicated by the reference character A in FIG. 2, a high dropletconcentration in the center of its frontal area as is illustrated inFIG. 3A. It can be seen in FIG. 3A that the concentration of thedroplets diminishes toward the outer edge of the spray.

When the paint-air stream reaches the area of the deflection tubes 11and 12-, such as at the point indicated by the reference character B inFIG. 2, the air injected laterally into the tube 4 through these tubes11 and 12 will compress the sides of the paint-air stream therebyspreading its center vertically so that some of the droplets that werein the center portion are now dispersed above and below it as isrepresented in FIG. 33. At this point, the pressure in the center of thepaint-air stream is slightly higher than the pressure in its upper andlower portions.

This pressure differential is considerably increased when the paint-airstream leaves the output end of the tube 4 and approaches the objectthat is to be coated, such as the magnetic recording tape 10 that ispositioned within the output opening 9 of the chamber 1. In order toachieve this increase in the pressure differential, each of the ducts i1and 12 is so located as to have a side portion extending a shortdistance outwardly beyond the output end of the tube 4. Because of thisconstruction, a portion of the opening of each of the ducts 11 and 12projects beyond the end of the tube 4 in the direction of the outputopening 9 as is shown in FIG. 2. Air from these projecting portions ofthe ducts 11 and 12 serves to further increase the above-mentionedpressure differential.

It is to be noted that air in this horizontal center area is preventedfrom flowing directly to the vacuum opening 13 by the curvilinear sidesof the ducts l1 and 12 which function as battles to direct the flow ofair over the top and bottom flat surfaces of the ducts 11 and 12. Thevacuum source 13 consequently draws a higher volume of air from the fourcorner regions of the output area of the chamber 1 than it draws fromthe horizontal center portion of this area. This action causes the upperand lower portions of the paint-air stream in this output area to begreatly widened or expanded with respect to the horizontal centerportion of the paint-air stream.

The resulting effect produced by this controlled environment at a pointlocated near the output opening 9 of the housing 1, such as the pointindicated by the reference character C in FIG. 2, is illustrated in FIG.3C. Here it can be seen that, while the suction created by the vacuumsource 13 has spread the horizontal center portion of the paint-airstream so that it is wider than it was at the point shown in FIG. 313,it also has, at the same time, considerably increased the extent of theupper and lower portions of the paint-air stream.

It can also be seen in FIG. 3C that the concentration of the paintdroplets along an imaginary vertical line at the output end of thehousing 1 opposite the center of the tube 4 is higher in the middle thanat either end. The distribution of the droplets is gradually reversed asthe hypothetical vertical line is moved laterally across the outputopening 9 toward either end thereof. For example, if the assumed line isplaced opposite the mid-point of either one of the ducts 11 and 12, thenthe center portion of the line will not contain any droplets as theywill be distributed only along the end portions of the line.

The extent of this reversal of the distribution of the droplets in thearea of the output opening 9 is determined by controlling or regulatingthe rate of entry of air coming into the chamber 1 from the deflectiontubes 11 and 12. This control is accomplished by adjusting the degree ofvacuum supplied through the vacuum opening 13 so that the higher densityof the droplets in the shorter horizontal center portion of the spray atthe output opening 9 is balanced or compensated by the longer lengths ofthe less dense upper and lower portions of the spray. In other words,although the density of the droplets in either the upper or lowerportions of the spray at this point is less than it is in the horizontalcenter portion, this lesser density is compensated by the fact that thelength of the horizontal centerportion is much less than the length ofeither the upper or lower portions of the spray. The end result obtainedfrom this balanced condition is that, when the above-mentionedhypothetical vertical line, or the tape 10, is moved across the outputopening 9 from one end to the other at a constant rate of speed, it willacquire an evenly dispersed coating of uniform thickness and density.

It can be understood from the above explanation that this desirableresult is dependent on the reshaping of the paint-air stream asdescribed above. The importance of reshaping the paint-air stream can beappreciated when it is recalled that the paint-air stream from the airbrush 5 initially has a high droplet concentration at its center portionas is illustrated in FIG. 3A. If no substantial change should be made inthis condition of the paint-air stream before it reaches the tape 10,then the resulting coating which would be formed on the tape 10 would bemuch thicker along its horizontal middle portion than it would be alongeither its upper or lower portions. The formation of such unevencoatings can be avoided by employing the spray system of this inventionin the controlled environment described above.

What is claimed is:

1. A spray system for producing a dispersion coating of uniformthickness and density on a surface of an object, said spray systemincluding in combination a housing defining a chamber for forming acontrolled environment for said spray system, said housing having at oneend means defining an output opening adapted to be positioned against atleast a portion of said surface, a hollow tube mounted in said chamberand having an input end protruding externally beyond another end of saidhousing for receiving both air and coating material in the form of apaint spray, said tube having an output end contained entirely withinsaid chamber and located near said output opening, a source of vacuumconnected into said chamber for drawing outside air into the input endof said tube for forming a paint-air stream, and means including aplurality of air ducts for increasing the pressure in the centralportion of said paint-air stream while reducing the pressure of itsopposite outer portions as it leaves the output end of said tube, saidair ducts being disposed in said chamber near said output opening andhaving output orifices entering into opposite sides of the output end ofsaid tube, each of said ducts having an input orifice at one end thereofprotruding externally outside said chamber for admitting outside air tothe output end of said tube, and each of said output orifices of saidducts being so constructed and arranged as to have a side portionthereof projecting beyond the output end of said tube in the directionof the output opening of said housing for increasing the differencebetween said pressures.

2. A spray system for forming a dispersion coating upon only a portionof a surface of an object, said spray system comprising a chamber havingat one end means defining an output opening adapted to enclose saidportion of said surface, a hollow tube mounted in said chamher andhaving an output end completely contained within said chamber andpositioned near said output opening, said tube having an input endprojecting externally beyond another end of said chamber for receivingboth air and coating material in the form of a paint spray, a source ofvacuum connected into said chamber near the input portion of said tubefor drawing outside air into the input end of said tube for forming apaint-air stream, said vacuum source also being adapted for drawing saidpaintair stream out of the output end of said tube and in a directionback into said chamber toward the input portion of said tube, and meansincluding a plurality of curvilinear baffles for expanding opposite endportions of the paint-air stream with respect to the center portionthereof when said paint-air stream leaves the output end of said tube,said bafiies being attached to opposite sides of the output end of saidtube and disposed transversely across the output portion of said chamberwith one side edge of each of said baffies protruding beyond the outputend of said tube in the direction of the output opening of said chamber,and each of said baffies having an input orifice so constructed andarranged as to protrude outside said chamber for admitting outside airto the output end of said tube for increasing said expansion of saidpaint-air stream.

3. A spray system for producing a dispersion coating of uniformthickness and density on a surface of an object, said spray systemincluding in combination a housing defining a chamber for forming acontrolled environment for said spray system, said housing having at oneend means defining an output opening adapted to be positioned against atleast a portion of said surface, a hollow tube mounted in said chamberand having an input end protruding externally beyond another end of saidhousing for receiving both air and coating material in the form of apaint spray, said tube having an output end contained entirely withinsaid chamber and located near said output opening, a source of vacuumconnected into said chamber for drawing outside air into said tube, andmeans including a plurality of air ducts disposed in said chamber nearsaid output opening and having output orifices entering into oppositesides of the output end of said tube, each of said ducts having an inputorifice at one end thereof protruding externally outside said chamberfor admitting outside air to the output end of said tube, and each ofsaid output orifices of said ducts being so constructed and arranged asto have a side portion thereof projecting beyond the output end of saidtube in the direction of the output opening of said housing.

References Cited in the file of this patent UNITED STATES PATENTS1,661,150 Birkenmaier Feb. 28, 1928 2,088,542 Westin July 27, 19372,270,579 Chamberlin et a1. Jan. 20, 1942 2,514,748 Di Stefano July 11,1950 2,646,313 Peeps July 21, 1953 FOREIGN PATENTS 846,841 France Sept.6, 1939 614,475 Great Britain Dec. 16, 1948

3. A SPRAY SYSTEM FOR PRODUCING A DISPERSION COATING OF UNIFORMTHICKNESS AND DENSITY ON A SURFACE OF AN OBJECT, SAID SPRAY SYSTEMINCLUDING IN COMBINATION A HOUSING DEFINING A CHAMBER FOR FORMING ACONTROLLED ENVIRONMENT FOR SAID SPRAY SYSTEM, SAID HOUSING HAVING AT ONEEND MEANS DEFINING AN OUTPUT OPENING ADAPTED TO BE POSITIONED AGAINST ATLEAST A PORTION OF SAID SURFACE, A HOLLOW TUBE MOUNTED IN SAID CHAMBERAND HAVING AN INPUT END PROTRUDING EXTERNALLY BEYOND ANOTHER END OF SAIDHOUSING FOR RECEIVING BOTH AIR AND COATING MATERIAL IN THE FORM OF APAINT SPRAY, SAID TUBE HAVING AN OUTPUT END CONTAINED ENTIRELY WITHINSAID CHAMBER AND LOCATED NEAR SAID OUTPUT OPENING, A SOURCE OF VACUUMCONNECTED INTO SAID CHAMBER FOR DRAWING OUTSIDE AIR INTO SAID TUBE, ANDMEANS INCLUDING A PLURALITY OF AIR DUCTS DISPOSED IN SAID CHAMBER NEARSAID OUTPUT OPENING AND HAVING OUTPUT ORIFICES ENTERING INTO OPPOSITESIDES OF THE OUTPUT END OF SAID TUBE, EACH OF SAID DUCTS HAVING AN INPUTORIFICE AT ONE END THEREOF PROTRUDING EXTERNALLY OUTSIDE SAID CHAMBERFOR ADMITTING OUTSIDE AIR TO THE OUTPUT END OF SAID TUBE, AND EACH OFSAID OUTPUT ORIFICES OF SAID DUCTS BEING SO CONSTRUCTED AND ARRANGED ASTO HAVE A SIDE PORTION THEREOF PROJECTING BEYOND THE OUTPUT END OF SAIDTUBE IN THE DIRECTION OF THE OUTPUT OPENING OF SAID HOUSING.